1. Field of the Invention
The invention relates generally to a motion detector and alarm system for actuating an alarm device in response to movement of an object, and more particularly to a portable motion detector and alarm system which is easy to install and operate and is capable of detecting motion relative to a variety of predetermined positions. Still more particularly, the invention concerns an improved inertial sensor that may be used in a motion detector and alarm system.
2. Prior Art
The problem of protecting homes, businesses and other premises against unauthorized intrusions is becoming increasingly important due to the increase in vandalism, theft and even physical attacks upon the inhabitants. Various prior art systems have been developed to address the problem and numerous examples exist of alarm or warning devices. One commonly used protective system involves wiring doors and windows in such a manner that an unauthorized opening of the door or window activates an electric circuit which in turn produces an alarm.
For example, U.S. Pat. No. 4,271,405 to Kitterman discloses an alarm control system for protecting a premises including a four conductor bus line leading from a master control station and extending about the interior perimeter of the premises. Sensors positioned near each port of entry to be monitored are connected in parallel relationship to the bus line. Each sensor carries a biased reel carrying line secured to a window, door, screen or the like. Disturbance of a sensor causes a magnetically responsive switch therein to generate a pulse triggering circuitry within the control station to activate the desired alarm device.
While effective, this system requires extensive wiring of the premises as a bus line must be routed about the interior perimeter of the premises between a master control station and the ports of entry at which the motion sensors are to be located. Hence, this system is time consuming and complicated to install, and installation may require expertise beyond that of the average home or business owner. Once installed, the sensors of this system are not easily relocated. Further, the system may be defeated by cutting the wires extending between the sensors and the master control station.
U.S. Pat. No. 3,781,836 to Kruper et al discloses an alarm system including a magnetic pulse generator for producing an output pulse in response to a change in magnetic flux in response to an intrusion of a designated area. A radio transmitter circuit responds to the pulse from the magnetic pulse generator by transmitting a signal to a remote receiver circuit which in turn generates a pulse for actuating an intrusion alarm circuit. The system requires a complex linkage assembly to translate motion of the object to motion of a magnet. In addition a relatively bulky pick-up coil assembly is necessary to generate the pulse to be applied to the transmitter circuit.
U.S. Pat. No. 3,696,380 to Murphy discloses a portable alarm device with a battery or low voltage operated sound signal triggered by a magnetic reed switch which is closed to complete the circuit by a magnet attached to a movably mounted arm, the poles of the magnet being positioned perpendicular to the longitudinal dimension of the contact strips of the reed switch to cause the reed switch to close when the magnet is in either of two positions relative to the switch.
A need remains for a motion detection and signal generating system which is small in size, easily transportable, easy to install and which can sense motion relative to any desired initial position of an object. An additional desirable capability of the foregoing system would be to provide information about the detected motion to the owner of the object, or a remote location such as a law enforcement or other security agency. It would likewise be desirable to provide identification information about a specific object whose motion has been detected in the event that the motion detection and signal generating system is implemented to detect motion at multiple locations (e.g., doors, windows) within a larger security area (e.g., a residence, an office or otherwise).